Even though daytime temperatures in the tropics of Mars can be about —20°C, a summer afternoon there might feel about the same as an average winter day in southern England or Minneapolis. That’s because there's virtually no wind chill on the Red Planet, according to a new study—the first to give an accurate sense of what it might feel like to spend a day walking about on our celestial neighbor.

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"I hadn't really thought about this before, but I'm not surprised," says Maurice Bluestein, a biomedical engineer and wind chill expert recently retired from Indiana University—Purdue University Indianapolis. The new findings, he says, "will be useful, as people planning to colonize Mars need to know what they’re getting themselves into."

There's no doubt that Mars is cold: Planet-wide, the average temperature is about —63°C, compared with Earth's more hospitable 14°C. Even in the martian tropics, nighttime temperatures can drop to near —90°C, says Randall Osczevski, an environmental physicist who recently retired from Defence Research and Development Canada in Toronto. Yet thermometer readings on Mars are highly misleading to earthlings, he notes. That's because people typically base their notions of comfort in cold, windy conditions on their personal experiences--all of which have taken place within our planet’s much thicker atmosphere.

At Mars's surface, atmospheric pressure is less than 1% that of air pressure on Earth at sea level. That's about the same pressure as Earth's atmosphere at an altitude of 32 kilometers—or about 2.5 times the cruising heights of jet aircraft, Osczevski says. But air that thin doesn't do a good job of carrying heat away, even when the winds are blowing at 100 kilometers per hour (as they sometimes do in the Red Planet’s global dust storms). In other words, he notes, on Mars the wind chill—the added cooling effect generated by air sweeping heat away from a body warmer than its environment—is almost nonexistent.